[Growth hormone receptor and dwarfism]

Laron syndrome is a rare autosomal recessive disease characterized by extreme resistance to growth hormone (GH). A GH receptor defect, which was hypothesized as the cause of the disease, was demonstrated after the cloning of the GH receptor cDNA. Several abnormalities of the GH receptor gene have been identified in the patients, demonstrating the genetic heterogeneity of the disease. Most of the identified mutations belong to the extracellular domain of the receptor, in the hormone-binding region, and this finding is consistent with the absence of GH binding activity found in the patients' plasma. Other mutations will be found, particularly in patients with Laron syndrome associated with a normal high affinity GH binding protein; in these cases, the defect could be at the dimerization level or at a later step in signal transduction. Laron syndrome represents a valuable model to identify structural and functional important regions of the receptor involved in GH action. In other situations of growth failure, such as in the Pygmies, a defect in the regulation of the GH receptor gene expression has been proposed.